1. Field of the Invention
The present invention relates to an optical film, a light reflective film, a liquid crystal display panel, a method and apparatus for producing an optical film, a method of producing a die roller, and a method and apparatus for laminating an optical film.
2. Description of the Related Art
Recently, application of a liquid crystal display panel to a word processor, a laptop personal computer, a pocket television, a portable telephone, and the like is rapidly advancing. Among liquid crystal display panels, a reflection type liquid crystal display panel and a semi-transmission type liquid crystal display panel in which light entering from the outside is reflected by a light reflective film receive attention because external light can be used so as to attain a lower power consumption, and the thickness and weight of the panel can be reduced.
In the field of a portable telephone and the like, a request for a multicolor display of a reflection type liquid crystal display panel is growing. Therefore, it is required to improve the performance of a light reflective film, and the brightness, i.e., the reflectance of a light reflective film becomes a critical point. As a high-performance light reflective film, known is a diffusive light reflective film in which concave and convex portions of a predetermined shape are formed in the surface of the light reflective film, thereby enabling light entering at various angles to be efficiently used. Therefore, it is expected to employ a diffusive light reflective film in which, in order to make reflected light from a light reflective film coincident with the visual angle of a liquid crystal display panel, concave and convex portions of the light reflective film are formed into a pyramidal structure having a predetermined inclination angle. A prior art of prism-shaped concave and convex portions having such a pyramidal structure is disclosed in Japanese Unexamined Patent Publication JP-A 11-147255 (1999).
As a method of producing a light reflective film having concave and convex portions, known are methods such as a photolithography method which is disclosed in Japanese Unexamined Patent Publication JP-A 11-248909 (1999), and an emboss method which is disclosed in Japanese Unexamined Patent Publication JP-A 10-311910 (1998), and in which a mother member is cut by a cutting device to form a matrix and the matrix is transferred to produce a light reflective film. Japanese Unexamined Patent Publication JP-A 2000-47199 (2000) discloses a method of producing a light reflective film. In the method, an roll-like original plate in which irregular concave and convex portions are formed in the surface is pressed against a resin layer to transfer the concave and convex shape of the original plate to the resin layer, and a reflection film made of aluminum and a thin film layer are laminated on the resin layer, thereby producing a light reflective film.
JP-A 10-311910 discloses a method in which moire fringes between a light reflective film and a display electrode are prevented from occurring, by randomly setting pitches of concave and convex portions.
In the production method disclosed in JP-A 11-248909 or JP-A 10-311910, an expensive apparatus is necessary for producing a light reflective film in which concave and convex portions are disposed with random pitches, and the productivity is lowered.
The irregular concave and convex portions in JP-A 2000-47199 cause a problem in that the directivity of reflected light is lowered. In a liquid crystal display panel, particularly, the liquid crystal has a visual angle direction, and hence the position where it is possible to see the display is inevitably restricted. In a light reflective film, therefore, it is not required to reflect light in a direction opposite to the visual angle direction, and it is desired to reflect also light which has been once reflected in the opposite visual angle direction, in the visual angle direction. Namely, a light reflective film is requested to have a directivity. In order to attain such a directivity of a sufficient level, the shapes and arrangement of the concave and convex portions must be regularly formed.
In a liquid crystal display panel having a light reflective film in which pyramids are arranged in a row to form a concave and convex shape, however, moire fringes are caused by the ridges of the pyramids and a row of pixel electrodes. Therefore, the ridges of the pyramids and the pixel electrodes must be arranged so as to be shifted from one another.
In the case where the row of pyramids is formed in parallel with an edge of the light reflective film, when the edge of the light reflective film is placed to be in parallel with an edge of a substrate, moire fringes are caused by the ridges of the pyramids and the row of pixel electrodes. In order to prevent such moire fringes from occurring, therefore, the light reflective film must be laminated obliquely with respect to the row of pixel electrodes.
In this case, when the light reflective film is laminated to the inside of the substrate as shown in FIG. 11, there is a region where the light reflective film does not exist, on the substrate. Therefore, the number of obtainable liquid crystal display panels is reduced and the productivity is lowered. When the light reflective film is laminated to the outside of the substrate as shown in FIG. 12, dusts are produced in a step of cutting portions of the light reflective film protruding from the substrate, and the dusts become foreign matters to lower the productivity. As shown in FIG. 13, in a step of laminating the light reflective film to the substrate, the substrate must be transported obliquely with respect to the light reflective film which is fed in a belt-like form from a roller. The work of this step is difficult to do.